In 3GPP Rel-7 network init PDP context procedures have been introduced. Since network wide support from terminals and SGSN and GGSN for network init procedures cannot be expected from day one a bearer control mode (BCM) procedure has been defined. BCM may be different depending on access type as follows:
For E-UTRAN access, EPS bearers are used. There are two flavors of EPS bearers default and dedicated. Dedicated Bearers are always established, modified and removed by the network. The GW is responsible to initiate, remove or modify an EPS bearer.
For pre rel-8 2G/3G access the PDP context may be established by the network or by the UE. The selection of the BCM depends on network and UE capabilities and is negotiated at IP-CAN session establishment and applies for all PDP contexts within that IP-CAN session. The selected bearer control mode may be modified during the lifetime of an IP-CAN session due to a UE moving to a SGSN not supporting the selected bearer control model. The BCM may be ‘NW-only’ or ‘UE-only’ or ‘NW and UE’.
However, in spite of the different bearer control modes and network capabilities, 3GPP Rel-8 has not considered yet the implications of attaching from accesses networks that handles the bearers in a different way and the handover cases between these networks.
The current PCC architecture specified the BCM negotiation. According to it, the PCRF decides the BCM to be used by the network, based on the network capabilities, the UE preferences and other possible criteria.
The Bearer Control Mode set to ‘UE-only’ means that the PCRF performs bearer binding The PCRF compare the TFT(s) of all IP-CAN bearers within an IP-CAN session with the generated PCC Rules waiting to be installed/modified or removed. The PCRF indicates to the PCEF the IP-CAN bearer within the IP-CAN session where the PCC Rules shall be installed or removed.
The Bearer Control Mode set to “NW-only” means that the PCEF performs bearer binding. The PCRF installs, modifies or removes PCC Rules over Gx interface to the PCEF. The PCEF checks if a bearer is established with the QCI and ARP indicated by the PCC Rule and associates these PCC Rules to the IP-CAN bearer that has the same QCI, ARP values.
In the BCM ‘NW-only’ the trigger to establish or modify a bearer is the PCRF installing PCC Rules over Gx. However, the PCRF may install PCC Rules either due to the UE requesting resources for a service or unconditionally when the service session information is received over Rx.
The Bearer Control Mode set to ‘UE-NW’ means that both the PCRF and PCEF performs bearer binding. PCRF performs the bearer binding for those services for which the UE requests a bearer establishment/modification and the PCEF performs the bearer binding for those services for which the PCEF requests a bearer establishment/modification.
There are also other non-3GPP legacy access networks where the bearer establishment may also be done by the User Equipment. One example is 3GPP2, where the standard solution is fully based on what 3GPP has defined in Release 7. Same considerations should then be taken into account for these cases.
Rel-8 EPS has defined a generic architecture that, in principle should allow the EPS user to access from different kind of access networks and perform inter-access handover.
The assumption for EPS is that PCC architecture corresponds to a bearer agnostic model where the GW is in charge of the bearer binding meanwhile PCRF will have the control at service level
The following problem with current PCC architecture can be seen:                1. No bearer control has been defined for Gxx interface. It means that for the GERAN/UTRAN access to EPS using PMIP in the S5 interface, there is no mechanism defined for negotiation of the BCM, nor having this negotiation at the PCRF. Consequently, both the BBERF and the PCRF assumes that the default BCM applies (‘UE-only’ as defined in Rel-7). The consequence is that it will not be possible to perform bearer binding at the BBERF for an EPS attached to EPS using a GERAN/UTRAN access network with PMIP over S5.        2. It is not specified any mechanism to change the BCM during the lifetime of the IP-CAN session. That means that it is unpredictable and may vary depending on the network implementation which the network behavior is when an UE attached to a network that works in UE-init mode moves to a network that works in NW-init mode. It may occur that existing bearers cannot be modified any longer or that the IP-CAN session cannot be retained.                    An IP-CAN session modification occurs for an IP-CAN session with BCM set to ‘UE and NW’ (e.g. in E-UTRAN):            An IP-CAN session modification occurs for an IP-CAN session with BCM set to ‘UE-only’:                        
If BCM is modified from ‘UE only’ to ‘UE and NW’, the bearer binding should be performed by the GW from now on. However, there are no mechanisms today to transfer such responsibility. Given the change of the bearer binding responsibility requires a mechanism how to maintain the existing bearers and installed PCC/QoS Rules, when a different bearer control mode is selected i.e. PCRF or GW responsibility.